SOUTH SAN FRANCISCO 
The pilots of Asiana Flight 214 relied on automated cockpit equipment to control the jetliner’s speed as they landed at San Francisco airport, but realized too late they were flying too low and too slow before the aircraft crashed, investigators said Tuesday.

The new details were not conclusive about the cause of Saturday’s crash, but they raised potential areas of focus: Was there a mistake made in setting the automatic speed control, did it malfunction or were the pilots not fully aware of what the plane was doing?

A puzzling aspect of the crash has been why the Boeing 777 jet came in too low and slow, clipping its landing gear and then its tail on a rocky sea wall short of the runway. The crash killed two of the 307 people on board and injured scores of others, most not seriously. Among those injured were two flight attendants in the back of the plane, who survived being thrown onto the runway when the plane slammed into the sea wall and the tail broke off.

National Transportation Safety Board chairman Deborah Hersman said the training captain who was instructing the pilot flying the aircraft has told investigators he thought the autothrottle, similar to a car’s cruise control, was programed for 137 knots — the target speed the pilots had selected for how fast they wanted the plane to be flying when it crossed the runway threshold. Instead, investigators said the plane reached speeds as low as 103 knots and was in danger of stalling because it was losing lift before it hit the sea wall.

The pilot told investigators he realized the autothrottle wasn’t engaged seconds before they hit. Their last-second efforts to accelerate the plane and abort the landing failed, although many survivors report hearing the engines roar before impact.

An overreliance on automated cockpit systems has figured in dozens of air crashes and incidents in recent years.

“Some people, if they believe the autothrottles are engaged and if they are used to flying with the autothrottle engaged, will not realize that the autothrottles are not engaged and will let the plane get pretty slow. That has come up before,” said John Cox, an aviation safety consult and former Air Line Pilots Association accident investigator.